Liquid crystal display (LCD) devices are well known and are useful in a number of applications where light weight, low power and a flat panel display are desired. Typically, these devices comprise a pair of sheet-like, glass substrate elements or "half-cells" overlying one another with liquid crystal material confined between the glass substrates. The substrates are sealed at their periphery with a sealant to form the cell or device. Transparent electrodes are generally applied to the interior surface of the substrates to allow the application of an electric field at various points on the substrates thereby forming addressable pixel areas on the display.
Various types of liquid crystal materials are known in the art and are useful in devices referred to as twisted nematic (TN), super twisted nematic (STN) and ferroelectric display devices. The ferroelectric liquid crystals are particularly useful due to their bistable characteristics and fast switching times. Ferroelectric liquid crystal materials and display devices incorporating these materials are described in U.S. Pat. No. 4,367,924 entitled "Chiral Smectic C or H Liquid Crystal Electro-Optical Device" and U.S. Pat. No. 4,563,059 entitled "Surface Stabilized Ferroelectric Liquid Crystal Devices".
It is desirable to be able to manufacture large area displays of relatively light weight for use in portable devices such as computers and with overhead projectors and the like. Certain organic, polymeric substrates are much lighter than glass while being transparent and are therefore preferred for use over glass in large area, lightweight displays. However, a problem with the use of polymeric materials as substrates for liquid crystal displays is that these substrates tend to be more flexible than glass and must be separated by a dense population of spacers in order to maintain uniform separation between the closely spaced substrates forming the liquid crystal display device. In order to produce a uniform electric field at low voltages and show uniform contrast across the entire display area, precise control of the shallow cavity containing the liquid crystal material is required. This problem is even more severe with surface stablized ferroelectric liquid crystal displays which require a nominal 2.mu.m spacing controlled to within 0.1 .mu.m for good results.
The prior art means for achieving the required spacing uniformity uses either precisely dimensioned, short-length polymeric fibers or spheres as in U.S. Pat. No. 4,501,471 or spacing members made of photoresist material bonded to the substrate as in U.S. Pat. No. 4,720,173. Each of these methods has deficiencies. Fiber and spheroidal spacing particles are not easily placed uniformly on the substrate to maintain even spacing over the entire area and fibers may overlap increasing the spacer height. Moreover, when the device flexes or is otherwise physically stressed, the spacers may shift or migrate to cause starved areas in the display cell. Bonded structural members require that they be precisely positioned on each substrate with exactly the same height, a feat that is difficult given the dimensions and tolerances required for effective liquid crystal displays. Members having different chemical composition from the substrate may suffer from differential thermal expansion causing possible fracture of the bond at the interface and shifting of the spacing member.
One drawback in extending present LCD manufacturing technology to larger areas is that it is dependent on the state of the art in large area photolithography (currently limited to less than 18 inches square) and precision polished glass technology. Presently, manufacturing yields for 4-inch diagonal display devices are low, sometimes less than 20% because of defects that can occur due to the large number of photolithographic steps involved. This poor yield translates into high display system cost. The cost of the much larger displays would be even greater.